a) Field of the Invention
The present invention relates to a method of forming a wiring layer including a titanium nitride (TiN) film, and more particularly to methods of evaluating a TiN film and of forming a tungsten (W) wiring layer, applicable to a method of forming a wiring layer having a TiN film as an underlying layer of a W layer.
b) Description of the Related Art
A wiring forming method is known which forms a TiN film as an underlying layer of a W plug or a W wiring. A TiN film of this kind is formed by reactive sputtering or CVD (chemical vapor deposition) in order to improve adhesion of a W plug or a W wiring.
Generally, intrinsic TiN has a stoichiometric composition ratio Ti:N of 1:1 with high crystallinity, providing a low resistivity of about 50 .mu..OMEGA.-cm like Ti. Metal Ti has a low resistivity. As Ti is nitrided and its nitridation progresses, the resistivity increases, and as the nitridation further progresses, the resistivity reduces to such values like that of Ti. Conventionally, if a measured sheet resistance of a TiN film has a predetermined value or lower, the TiN film has been evaluated to be good.
With this evaluation method, however, a Ti rich TiN film having a low nitridation degree can be judged to be good because its sheet resistance is low. The evaluation results therefore are low in reliability and precision.
If a W plug or W wiring layer is formed on a TiN film having a low nitridation degree, sufficient adhesion between the TiN film and the W plug or W wiring layer cannot be obtained.